Electron beam tubes, such as klystrons and inductive output tubes (IOTs), conventionally comprise three basic elements. Those elements are: an electron gun structure, an rf interaction region and an electron beam collector. Although the invention applies to all types of electron beam tubes it will be described, without loss of generality, with reference to an IOT.
In an IOT, the electron beam is density modulated in the electron gun stricture. The beam passes to the rf interaction region, where rf power is extracted by a resonant cavity system. For TV broadcast applications this consists of a primary cavity attached to the tube and coupled to a secondary cavity (also called an output cavity). Power is coupled from the secondary cavity to an appropriate output feeder line. After passing through the rf element the electron beam impinges on the electron beam collector, the remaining energy of the beam being dissipated on the walls of the collector.